This invention relates to a method for the manufacture of a heavy duty elastomeric bearing of the kind comprising a sandwich arrangement of layers of elastomeric material interposed by metal reinforcing layers and in which the metal layers are protected from the operating environment of the bearing during subsequent use by a cover layer of flexible material which extends over the otherwise exposed edges of the metal reinforcing layers.
One established construction of a heavy duty elastomeric bearing is described in the specification of GB-A-2190970 and comprises a stack of a plurality of superimposed metal reinforcing layers each of part-spherical shape and spaced from one another by intervening layers of rubber. The rubber and metal layers are each of an annular form and the assembly of said layers lies sandwiched between and bonded to inner and outer, generally axially spaced, rigid annular end members whereby the resultant elastomeric bearing is suitable for example for securing a vertically extending pipeline to structure on the seabed and to permit relative conical movement therebetween as also described in GB-A-2190970. The radially inner and outer edges of the metal reinforcing layers are covered by layers of protective elastomeric material so that fluid flowing through the pipeline cannot come into direct contact with radially outer edges of the metal layers and so that the surrounding sea environment cannot contact radially inner edges of the metal layers.
The fatigue strength of a heavy duty elastomeric bearing such as of the kind described in the preceding paragraph is dependent on a number of factors including the thickness of the respective rubber layers between the metal layers and between the metal reinforcing layers at each end of the stack and said inner and outer rigid members. If the thickness of a layer of elastomeric material departs significantly from the intended design thickness, for example if the thickness varies in any one layer at different points around the circumference of that layer, the fatigue life of the bearing is adversely affected.
Although in manufacture of the bearing the thickness of elastomeric material provided between successive metal reinforcing layers may be accurately controlled during a building process in which the successive metal and elastomeric layers are applied about a former, it is found that during subsequent vulcanization under the action of heat and pressure the thickness of the elastomeric layers can vary in an unpredictable manner to result in an adverse effect on potential fatigue life of the bearing.